1. Field of the Invention
This invention relates to deformable reflectors and more particularly to optical trihedral deformable reflectors formed of three planar mirrors forming, in twos, orthogonal dihedrons at 90.degree..+-..epsilon.. Such reflectors, when illuminated by a beam from a light source, have the property of reflecting the light toward the source after reflection on each of the three faces thereof, even though trihedron orientation varies over a wide range.
The reflected light beam is cone shaped, focused on the source, with a divergence angle 2.delta. substantially proportional to the orthogonality defect .epsilon. of the dihedrons. The reflected light illuminates a photoelectric receiver placed near the source over an angle inversely proportional to the square of the dihedron orthogonality defect, .epsilon..sup.2. Any variation in .epsilon. results in a variation in the illumination.
2. Description of the Prior Art
U.S. Pat. No. 4,319,804 discloses a hollow retroflector having three front optically flat reflecting surfaces arranged essentially in orthogonal reference planes. Each surface is on a plate having a pivotal axis perpendicular to one of the reference planes and has an adjusting device remote from its pivotal axis for fixing the plate in a position that is adjustable about its respective axis. The adjusting device and the means that establishes the pivotal axis cooperate with portions of the plates that are outside the aperture of the retroflector.
U.S. Pat. No. 3,873,191 issued Mar. 25, 1975, commonly assigned with the present invention, discloses a process for producing optical trihedrons having high precision qualities as regards orthogonality. In this procedure, a tetrahedral print is made by initially hollowing out a material (mould) using a stamp; then a tetrahedral model made of glass, silicon or any other hard material is machined by using conventional tooling to the desired accuracy 90.degree..+-..epsilon.. The three faces of the trihedron in the model are gold plated by vaporization in a vacuum under special conditions. This male model is then inserted in the mould print with a resin interlay. After resin cure, the model merely has to be extracted; the resin and the layer of gold remain fixed inside the print. A hollowed trihedron replica is thus obtained having exactly the same shape as the model.
Generally speaking, the aim is to obtain a trihedron with a stable shape and the mould is made of stabilized metal. For general purpose use, the trihedrons produced along these lines have an angle of divergence 2.delta. lying between 8 and 50 seconds of an arc.